You can only dream of an SUV with agility of a sports-car. Not possible! Laws of physics are above all. No tech or engineering can't overrule them.
"Driving pleasure" is not an absolute term. It's unique in every segment. Only a comparison within segment is possible. It's stupid to argue X6 is not as agile as eg. 6er, or 7er not as 1er. Size & weight do matter.
So ... X6 is is very capable, very agile, very dynamics, very sporty ... FOR AN SAV!!! Best in a segment. But don't be so naive to compare an SUV (although with a coupeish body) with a sports-car.
If you want to experience true driving pleasure, buy a potent, small, light, low sports performance coupe. 911 is a legend with a reason.
But some customers just want an extremely sporty & dynamic SAV(ish) vehicle. And X6 seems to be the best choice for those people.
PS: why weight increase? People want more & more convenience features, more safety features, more luxury features etc. And all that equipment does add weight. And people want more & more power. BMW can easily produce a light car with less power - but that's not what customers in premium segment want (especially not in Asia, ME & USA!). Therefore cars are heavier every time - or at least as heavy as predecessor (due the usage of lightweight materials). Do not blame the car makers - blame the customers: car makers only produce what the majority of customers want. And to sell they have to produce what customers want. That's business. Engineers are victims of marketing.